The invention relates generally to battery charging methods. More specifically, the invention concerns a charging method for the battery pack of an electric vehicle.
A known charging method for the batteries of electric vehicles utilizes three basic steps. The first step, with reference to the flow chart of FIG. 1, charges the battery pack to full power until a reference voltage (which may be temperature compensated) is reached, as shown in steps 102, 104, 106, 108 and 110 of FIG. 1.
In a second step, charging continues holding the voltage at the reference voltage as the charging current decreases over time, as seen in steps 112, 114, 116 of FIG. 1.
In a third step, charging is carried out at a constant current with charging complete determined as a function of a time value determined by the time spent in the first two steps, as seen from steps 118, 120, 122, 124 and 126 of FIG. 1.
This known method performs satisfactorily when the vehicle batteries are in daily use, but is unacceptable for long periods (e.g., two weeks or more) of vehicle non-use. Furthermore, the known method has no capability for recovering a vehicular battery pack from a deep discharge.
Therefore, there is seen to be need in the art for a vehicular battery charging method capable of maintaining a desired vehicle operating range, increasing battery pack life and recovering from a long non-usage period or deep discharge.